China's Huawei recently unveiled a 6.1in handset, but it was only a 720p display.

They add to the so-called "phablet" category, as manufacturers test how big customers are willing to go.

When Samsung helped pioneered the format with its 5.3in Galaxy Note in 2011, many analysts suggested its size was too large to find favour.

Dell had previously released a 5in phone - the Streak 5 - but had ended up discontinuing the line to focus on a larger 7in tablet.

But the Note proved a success for the South Korean firm, leading Samsung to announce a larger successor last August.

In recent months other firms, including Sony, LG, HTC and ZTE, have unveiled smartphones with 5in and larger screens. More super-sized handsets are expected to be announced at the Mobile World Congress in Barcelona which begins on 25 February.

Remote control

Technology consultancy Ovum suggested that demand for the format was proving particularly strong in emerging markets where most customers could not afford both a phone and a tablet.

"The Galaxy Note has been a proof-point that consumers will adopt the larger phone," said the firm's researcher Adam Leach.

HTC offers a remote for its 5in handset in China

"It's an artificial barrier that a phone has to be below 5in and a tablet above 7in.

"There is a limit on what can be used with one hand, but there's an economic point that if a device can be used like a tablet and a phone then it's got more value, especially to people who can only afford to buy one device."

The popularity of phablets is taking some manufacturers in unexpected directions.

Taiwan's HTC recently announced it would bundle a bluetooth remote control with its 5in-screened Butterfly handset in China.

The add-on HTC Mini has its own screen and can be used to make calls or send messages when paired with the larger phone.